When Arizona’s notorious immigration law passed two years ago—seemingly out of nowhere—supporters said the measure would merely “mirror” and “assist” federal immigration enforcement. S.B. 1070, which comes before the U. S. Supreme Court this week, in fact contained harsh new criminal penalties against immigrants in an effort to achieve “attrition through enforcement,” as the state of Arizona puts it. (Or, as Mitt Romney has called it, self-deportation.) The Supreme Court will consider the four provisions of S.B. 1070 blocked by a federal district judge in July 2010: provisions that require state and local police to try to determine the immigration status of anyone detained if reasonable suspicion exists that they are in the United States illegally; that criminalize an immigrant’s failure to register with the federal government and carry a registration card; that make it illegal for undocumented immigrants to work or solicit work; and that permit state and local police to arrest immigrants without warrants if there is probable cause to deport them because they have committed a crime. At stake is whether federal law trumps—and thus invalidates—these contested elements of state law.